The present invention relates to metal lines semiconductor devices and to methods for forming the same, and more particularly, to a metal line having of a MoxSiy/Mo stacked diffusion barrier that inhibits copper diffusion.
Generally, metal lines are in a semiconductor device to electrically connect together various elements or lines with each other. Contact plugs are formed to electrically connect together lower metal lines and upper metal lines to each other. As the high integration of semiconductor devices continues to proceed, the aspect ratios of contact holes in which contact plugs are formed also gradually increases. As a result, the process for forming metal lines and contact plugs become more difficult because these diminutive metal lines and contact plugs must also maintain their physical and performance characteristics such as assuring that unwanted impurities do not diffuse past their respective corresponding diffusion barriers.
Aluminum and tungsten have been mainly used as suitable conductive materials in the metal lines of a semiconductor devices because they exhibit relatively good electrical conductivity properties and because they do not tend towards adversely affecting the performance of the resultant semiconductor device due to unwanted diffusion away from these metal lines. Recently, research has been made in the hopes of using copper as a next-generation material for a metal line because copper exhibits a superior electrical conductivity and a corresponding low resistance as compared to aluminum and tungsten. Copper (Cu) can therefore solve or at least aid in minimizing the problems associated with RC (resistance-capacitance) signal delay in the semiconductor device having a high level of integration and high operating speed.
It is known that copper diffuses rapidly through semiconductor substrates as well as through insulation layers. Further, the diffused copper is known to act as a deep-level impurity in the semiconductor substrate made of silicon and can induce leakage currents. Therefore, it is necessary to form a diffusion barrier at an interface between a copper layer acting as a metal line and the surrounding insulation layer.
Hereinbelow, a conventional method for forming a metal line of a semiconductor device will be briefly described.
After forming an insulation layer on a semiconductor substrate, a metal line forming region is defined by etching the insulation layer. Then, a diffusion barrier is formed on the insulation layer and on the surface of the metal line forming region, and a copper seed layer is subsequently formed on the diffusion barrier. Next, after forming a copper layer on the copper seed layer, a metal line comprising the copper layer is formed by CMPing (chemically and mechanically polishing) the copper layer.
However, in the conventional art described above, as the size of cells decreases in conformity with the trend toward higher integration of these semiconductor devices, the thickness of the diffusion barrier should also decrease. Therefore, it is becoming more difficult to properly prevent the diffusion of a copper constituent by means of the diffusion barrier formed in accordance to the conventional art techniques. Furthermore, in the conventional art described above, it is becoming more and more difficult to increase the thickness of the diffusion barrier so as to improve the characteristics of the diffusion barrier and thereby as a result the characteristics of the subsequent diffusion barrier deteriorate. In addition, in the conventional art described above, an unwanted overhang phenomenon can occur due to the conglomeration of the copper seed layer formed on the diffusion barrier. Because of this conglomeration of copper, the entrance to the metal line forming region is prone to being clogged, and as a consequence unwanted voids can be created in the metal line and thus the characteristics of the metal line can deteriorate.
As a result of fabricating metals lines using the conventional arts as described above, the characteristics and the reliability of a semiconductor device become compromised.